FAQ: What are the precautions to prevent latch-up on the AD8375?

Document created by Qui Employee on Sep 20, 2011Last modified by AndyR on Jan 31, 2012
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Q.

What are the precautions to prevent latch-up on the AD8375?

 

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A.

The outputs of the AD8376 are open collectors that need to be pulled up to the positive supply.  This can be done via chokes to VDD or resistors.  When using resistors the voltage drop across the resistors needs to be accounted for therefore the higher pull up supply.  The circuit showing the 9V is configured correctly.  The 9V minus the drop across the resistor results in the output of the AD8376 sitting at 5V.  The chokes pulled to 5V does the same exact thing.  For wide band applications the resistors are the best option because you’re not bandwidth limited by the parasitic capacitance and inductance of the chokes.  However leaving the 9V supply on while the part is powered down will cause the output pins to go to 9V. This will turn on the esd protection diodes as well as exceed the break down voltage of the output transistors. So it's necessary to ensure that the 9V supply is only on when the device is powered up.  One option is to  install 6.5  volt  clamps from the outputs to ground. So when the part is powered down, the current would go to about 50ma total.

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